Sensitivity of tobacco caterpillar, Spodoptera litura, to extract from a medicinal plant, Withania somnifera

ABSTRACT

The larval stage of a polyphagous moth Spodoptera litura (Lepidoptera: Noctuidae), commonly known as tobacco caterpillar, causes loss in many vegetables. Use of chemical pesticides to control this pest has resulted in environmental pollution, is hazardous to non-target organisms, and contributes to development of pest resistance against these compounds. Alternatives for pest management need to be developed. Extracts derived from plants can function as insect growth regulators and are easily biodegradable. Topical administration of root extracts from a medicinal plant, Ashwagandha (Withania somnifera L. Dunal), to sixth instar larvae and freshly molted pupae (0–2 h old) of S. litura caused prolongation of larval-pupal and pupal-adult ecdysis duration, mortality, reduced pupation, and adult emergence. Root extracts of W. somnifera produced the morphological and developmental abnormalities like ecdysial failure, formation of larval-pupal and pupal-adult intermediates, abnormal pupae and adultoids. Treatment with root extracts of W. somnifera was more toxic to pupae compared to larvae of S. litura. The results may be due to interference with normal hormonal mechanism eventually leading to disruption of molting and metamorphosis.

KEYWORDS:

• Withania somnifera
• ashwagandha
• ecdysial failure
• larval-pupal intermediates
• pupal-adult intermediates